DGLA is an industrially-important fatty acid that can be used for pharmaceutical and nutritional applications, in feed for aquaculture and animals and for enhancing their immunological systems thereby reducing their mortality and morbidity due to stress and diseases. DGLA, also known as 8,11,14-eicosatrienoic acid, is found only in microorganisms and always at low percentages. Usually, it serves as an intermediate in the biosynthesis of arachidonic acid (AA, 20:4ω6), the conversion of DGLA to AA being facilitated by the enzyme Δ5 desaturase.
Microalgae are a “green” and renewable source of biochemicals. They can be cultivated phototrophically or adapted, or engineered for growth under heterotrophic conditions.
Under conditions of nitrogen starvation, the content of AA can reach 21% of dry weight.
Plant oils are capable of producing various PUFAs. However, those produced by higher plants are restricted to chains of up to 18 carbon atoms. Microalgae on the other hand, are known to produce PUFA of up to 22 carbon atoms long.
Both AA and DGLA are PUFA of significant pharmacological interest. DGLA is found in many organisms as an intermediate; however, there are few natural host organisms in which there is accumulation of significant amounts of this PUFA. Possibly the only such source is a Δ5 desaturase deficient mutant of the fungus Mortierella (U.S. Pat. No. 6,602,690). However, one drawback associated with the PUFAs produced by this fungal mutant is the unfavorably low DGLA/AA ratio (approximately 12). A further disadvantage of the fungal-derived PUFAs is that they are susceptible to oxidation and synthetic antioxidants need to be added to prevent deterioration by oxidation. Since the oxidation is a chain reaction, even a small amount of oxygen can destroy PUFA rapidly.
A need thus exists for a natural, “green” source of DGLA that overcomes the aforementioned problems.